Considerable effort has been directed at producing an effective, non-stick and non-wetting coating on the surface of an inorganic article, in particular a utensil for preparing and/or serving food. The term "non-stick" signifies a surface that resists adherence of foreign substances, such as food. This property permits easy cleaning of dishes in which foods are cooked or baked. The term "non-wetting" indicates a surface that repels liquids such as water. The property is evidenced by a large contact angle between a drop of water and the surface on which the drop rests. An advancing angle of at least 90.degree. is considered as representative of a non-wettable surface.
Non-stick, non-wetting articles are commonly produced by coating article surfaces with a polytetrafluoroethylene (PTFE) layer. For example, U.S. Pat. No. 4,683,168 (Hares et al.) describes a process for coating glass or glass-ceramic articles with such a layer to produce non-stick cooking utensils. However, PTFE coatings exhibit the disadvantage of being opaque. Also, they require a thermal sintering process at 350.degree.-400.degree. C. for their production, are relatively expensive to produce, and do not provide a desired degree of abrasion resistance.
French Patent No. 2674862 (Carre) discloses an alternative material system and process for producing durable, non-stick and water repellent coatings on glass and glass-ceramic surfaces. The process involves applying a mixture of a selected silane with a lower alkanol and water which may be acidified. The silane has the formula R.sub.n SiX.sub.4-n, where R is an alkyl radical and X is a hydrolyzable alkoxy or chloro group. The mixture is applied to a surface containing hydroxyl groups, the silane is hydrolyzed and the alkanol-water mixture eliminated to form a polysiloxane coating adhering to the surface.
Numerous other processes and material systems have been proposed for rendering inorganic surfaces, particularly vitreous surfaces, non-sticking and water repellent. The desired properties can be obtained initially. However, there has persisted a problem with respect to wear during use, in particular, scratching by cleaning agents. It is, then, a purpose of the present invention to improve on the Carre process bv imparting a greater abrasion resistance to the coating there disclosed